Miniature, inert solenoid valves are used extensively in scientific instrument application. Here they are used to control and select high purity and aggressive fluids which have low flow requirements.
Oftentimes a plurality of individual solenoid valves are mounted on a miniature, inert mounting block known as a manifold. The manifold body includes a multiplicity of mounting surfaces upon which individual valves are mounted. Interior to the manifold body is a common passage connecting all valve mounting surfaces to a single source or return; and, a number of branch passages connecting individual valves with its respective fluid source or instrument.
Heretofore manifold assemblies were sold as a unit. The valves were permanently mounted to the manifold body. Thus, if an individual valve in a multiple grouping began to malfunction, the entire manifold assembly, including properly functioning valves, was removed from the test rig and replaced with a complete, substitute assembly. The removed assembly would then be returned by the user to the manufacturer for testing, repair, and/or replacement of the defective valve. This necessarily resulted in high costs for such assemblies.
Various mounting techniques have been employed to secure the valve to the manifold body. In interfacing the valve to the manifold body, it is obviously important that the fluid orifices in the valve communicate with the corresponding openings in the manifold body. In existing units typically, the manifold mount body portion of the valve includes a centrally disposed, threaded valve stem. It includes a first opening which communicates with its counterpart in the manifold body when the valve stem is threaded into a complementing threaded hole in the manifold body. An annular groove or channel is radially disposed in the manifold mount body portion at a distance from the center of the valve stem opening. The channel overlies a second opening in the manifold mount body portion which is connected to the first opening in one portion of the activated valve. A second complementing opening in the manifold body is disposed on the interfacing surface so as to be aligned with the groove in the manifold mount body portion. Elastomeric O-rings disposed on either side of the annular groove in the manifold mount body portion of the valve member isolate the channel so that there is no leakage of the sampled fluid between the first and second openings in the manifold body.
This mounting arrangement unfortunately results in an increase in what is known as dead volume. Dead volume is the potential volume within the manifold-valve assembly in which residual fluids may remain after a test sample is processed. This is an undesireable characteristic in that the contamination of subsequent samplings is increased. Also, sampling data results may be erroneously affected. The dead zone problem is further exacerbated when this mounting technique is used with an inline manifold due to comparatively high internal passageway lengths as contrasted with radial design, manifold bodies.
It is therefore a primary object of this invention to provide a valve-manifold body interface and assembly which permits ready replacement of individual, defective valves without the need to recalibrate an entire multiple valve-manifold assembly.
It is another object of the invention to provide a valve-manifold body interface which significantly minimizes the dead zone problem.
It is still another object of the invention to provide a valve-manifold assembly which minimizes the dead zone problem.